introduction to kidney and renal function

Question 1

functions of the urinary system

Answer 1

excretion - removal of organic waste products from bodily fluids
elimination - discharge of waste into environment

Question 2

essential renal functions

Answer 2

excretion 
of endogenous waste products 
of drugs and metabolites 
homeostasis 
water and electrolyte balance 
acid base balance 
regulation 
production of hormones eg erythropoietin and renin

Question 3

renal dysfunction

Answer 3

reduction in renal excretory function (uraemia, aztoaemia, drug toxicity)
inability to maintain salt and water balance and acid base balance (metabolic consequences)
compromised hormone function (anaemia, hypertension etc)

Question 4

how can kidneys fail (2 ways)

Answer 4

essential for life, if severe and untreated can = death
may be rapid (acute kidney injury, 10%) or may take months or typically years to develop chronic kidney disease (90%)
supplemented artificially by dialysis or transplant

Question 5

where are the kidneys found

Answer 5

paired organs
posterior abdominal wall
behind peritoneum
on either side of vertebral column
erach kidney 120-170g, approx 11cm long, 6 cm wide, 3 cm thick
joined at medial side to renal artery and vein, nerves and ureter

Question 6

organisation of the kidney

Answer 6

two main layers
cortex (outer, about 1.25 million nephrons) and medulla (inner, functional unit, responsible for urine formation and composition - pyramids drain into pelvis into ureters)

Question 7

what is the nephron

Answer 7

basic functional unit 
dec with age 
5 distinct sections 
glomerulus (renal corpuscle)
proximal tubule (PT)
Loop of Henle (LOH)
Distal tubule (DT)
Collecting duct (CT)

Question 8

what are the two types of nephrons

Answer 8

cortical and juxtamedullary

Question 9

what are cortical nephrons

Answer 9

70-80%
located in cortex
short loop of hence into medulla

Question 10

what are juxtamedullary nephrons

Answer 10

closer to medulla

loop of hence extends deep into renal pyramids

Question 11

what is the blood supply to the kidney

Answer 11

receive 20% CO
required for energy consuming transport processes
enter renal artery branches and leaves via renal vein also branches before leaving

Question 12

pathway of blood into kidneys

Answer 12

renal artery 
segmental
interlobar 
arcuate 
afferent arterioles 
interlobular 
to nephron (glomerulus to peritubular capillaries) to venules 
interlobular
arcuate
interlobar 
to renal vein

Question 13

blood supply to nephrons

Answer 13

afferent in and efferent out
peritubular capillaries in cortical
peritubular capillaries at top to vasa recta

Question 14

sympathetic supply to kidneys

Answer 14

postganglionic from sympathetic chain and fibres from coeliac ganglion
supplied arteries, afferent and efferent arterioles and granular cells
reduces blood supply to kidney during stress

Question 15

parasympathetic supply to kidney

Answer 15

from vagus nerve (ganglion in hilum)
many control tone of efferent arterioles
may modify glomerular filtration rate and renal blood flow
controversial

Question 16

main functions of the nephron

Answer 16

filtration of blood =filtrate
reabsorption of water, ions and organic nutrients from filtrate
secretion of waste into tubular fluid

Question 17

how do the nephrons work

Answer 17

transcellular transport (through cells)
paracellular transport (between cells)

Question 18

how does glomerular filtration occur

Answer 18

initial step in urine filtration
all small molecules filtered eg electrolytes, AAs, glucose, metabolic waste, some drugs and metabolites
cells and large molecules stay in blood eg RBCs, lipids, proteins, most drugs and metabolites

Question 19

how does tubular reabsorption occur

Answer 19

99% water, electrolytes and nutrients reabsorbed
some (Na+) via conc/electrochemical gradients
others co-transport (eg glucose and Na+)
water follows passively via osmosis (created by solute reuptake via aquaporins)
req ATP (Na+ reabsorption via Na+/K+ ATPase transporter)

Question 20

how does tubular secretion occur

Answer 20

some substances can’t be filtered - too big or protein binding
specialised pumps in PT can transport compounds from plasma into nephron for excretion
two kinds of pumps

Question 21

what are the two pumps involved in tubular secretion

Answer 21

for organic acids or drugs (eg uric acid, diuretics, antibiotics like penicillin)
for organic bases or drugs (eg creatinine, procainamide)